The Internet, a world-wide-network of interconnected computers, provides multimedia content including audio, video, graphics and text that typically requires a large bandwidth for downloading and viewing. Most Internet Service Providers ("ISPs") allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network ("PSTN") at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others.
Cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial ("HFC") cable system which have data rates of about 10 Mega-bits-per-second ("Mbps") to 30+ Mbps. These data rates are much higher than the data rates available on the PSTN.
With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie, Ill., and others offer customers higher-speed connectivity to the Internet, an intranet, Local Area Networks ("LANs") and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a "downstream" data rate of 30+ Mbps.
Cable television networks developed as unidirectional cable systems, supporting only a "downstream" data path. A downstream data path is the flow of data from a cable system "headend" to a customer. A cable system headend is a central location in the cable television network that is responsible for sending cable signals in the downstream direction. In order to use the cable system for data communication, a return data path must be provided. While bidirectional cable systems ("upstream" and "downstream" path over cable) are growing in number, many data over cable systems still use a return data path via a telephone network, such as a Public Switched Telephone Network. A cable television system with an upstream connection to a telephony network is called a "data-over-cable system with telephony return."
An exemplary data-over-cable system with telephony return includes a cable modem termination system, a cable television network, a public switched telephone network, a telephony remote access concentrator, a cable modem, customer premise equipment (e.g., a customer computer) and a data network (e.g., the Internet). The cable modem termination system and the telephony remote access concentrator together are called a "telephony return termination system."
The cable modem termination system receives data packets from the data network and transmits them downstream via the cable television network to a cable modem attached to the customer premise equipment. The customer premise equipment sends responses data packets to the cable modem, which sends response data packets upstream via the public switched telephone network to the telephony remote access concentrator, which sends the response data packets back to the appropriate host on the data network. The data-over-cable system with telephony return provides transparent Internet Protocol ("IP") data traffic between customer premise equipment, a cable modem and the data network (e.g., the Internet or an intranet). As is known in the art, IP is a routing protocol designed to route traffic within a network or between networks.
When a cable modem used in the data-over-cable system with telephony return is initialized, it will make a connection to both the cable modem termination system via the cable network and to the telephony remote access concentrator via the public switched telephone network. If the cable modem is using telephony return, it will acquire telephony connection parameters on a downstream connection from the cable modem termination system and establish a Point-to-Point Protocol ("PPP") connection to connect an upstream channel to the telephony remote access concentrator. As is known in the art, PPP is used to encapsulate datagrams over a serial communications link. After a PPP connection is established, the cable modem negotiates a telephony IP address with the telephony remote access concentrator. The telephony IP address allows the customer premise equipment to send IP data packets upstream to the telephony remote access concentrator via the public switched telephone network to the data network.
The cable modem also makes an IP connection to the cable modem termination system so that IP data received on the cable modem termination system from the data network can be forwarded downstream to the customer premise equipment via the cable network and the cable modem.
Once an IP address is obtained on the cable modern termination system, the cable modem obtains the name of a configuration file used to complete initialization. The cable modem downloads a configuration file from a central location in the data-over-cable system using a Trivial File Transfer Protocol ("TFTP") server. As is known in the art, TFTP is a very simple protocol used to transfer files, where any error during file transfer typically causes a termination of the file transfer.
In a typical network, such as an Internet, a subnet, or an intranet, a Dynamic Host Configuration Protocol ("DHCP") is used by a network device to obtain an IP address on a DHCP server from which configuration parameters are obtained. The IP address and the configuration parameters are used by the device to communicate with any other device that is connected to the network. One advantage of using the DHCP to obtain IP addresses is that other configuration information that is important to the network device may be obtained in a single exchange of messages. These messages include the DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACKNOWLEDGE and are documented in Request for Comments ("RFC"), RFC-2131 and RFC-2132, which may be obtained from the Internet Engineering Task Force ("IETF").
The DHCP provides IP addresses to clients in several scenarios. In one, the client chooses the IP address that is communicated by the DHCP in the DHCPOFFER message in response to a DHCPDISCOVER message. The DHCP client then sends a DHCPREQUEST message and, if the DHCP server accepts the request, the server sends a DHCPACKNOWLEDGE message. At that moment, the IP address is assigned to the client.
If a previous communication had been made by the network device to the DHCP, a previously assigned IP address may be retrieved in a DHCPOFFER message. A desired IP address may also be requested in the DHCPDISCOVER message even if an IP address is requested, the network device has no choice over the address selected.
Some networks, such as telco-return cable modem networks, are comprised of a large number of network devices. It is desirable to manage the network devices from a central network administrator. It would be desirable to manage the IP addresses of the network devices in the central network administrator but distribute the IP addresses locally. The network devices are also identified by a client identifier. The client identifier may be passed to the DHCP server which uses the client identifier as an index to the DHCP database. There is therefore no way to easily determine the network devices to which the IP addresses are assigned.
It would be desirable to distribute the IP addresses from local sources but at the same time, retain the IP address allocated in the central server (DHCP server). In this manner, the IP addresses will be distributed using an entity external to the DHCP while benefiting from the other resources available from the DHCP.